Conventional positive-working photosensitive polybenzoxazole compositions contain an alkaline soluble PBO precursor and a diazoquinone photoactive compound as disclosed in U.S. Pat. No. 4,371,685. The diazoquinone compound inhibits the solubility of PBO precursor in an aqueous base. However after exposure to light, the diazoquinone compound undergoes photolysis and converts to indene carboxylic acid, which promotes solubility of the PBO precursor in the aqueous base.
The chemically amplified positive-working photosensitive polybenzoxazole compositions containing a PBO precursor in which some of the phenol groups were protected with acetal protecting groups, and a compound which produces acid upon exposure to radiation (PAG) was disclosed in U.S. Pat. No. 6,143,467. After irradiation with light of appropriate wavelength, the PAG produces acid, which removes the acetal protecting group from the phenol moiety. This process promotes dissolution of the PBO precursor in aqueous base. However, the PBO precursor described in U.S. Pat. No. 6,143,467 contains amino end groups, which react with photolitically produced acid and slows photospeed. The PBO precursor of the present invention does not have amino end groups, which significantly improves the imaging performance of the chemically amplified formulation disclosed in the present invention.
US 2003/0087190 A1 describes an end capped PBO precursor in which some of the hydroxyl groups on the polymer backbone were blocked by tert-butoxycarbonyl moieties the present invention relates to end capped PBO precursors blocked with different moieties.